Kai-Uwe Hinrichs2and Jürgen Rullkötter2

ABSTRACT

Preliminary lipid analyses of Amazon Fan sediments
focused on the general characteristics of bitumen
composition. Of particular interest was the
identification of distinct sedimentary facies on a
molecular level. We investigated sediments from different
fan environments (pelagic and hemipelagic sediments as
well as active channel-levee sediments). On a qualitative
molecular level (i.e., types of compounds detected),
bitumen compositions of different fan environments are
very similar to each other.

Relative differences in bitumen distribution in terms
of marine vs. terrigenous origin appear to be
significantly correlated with the dilution of the
autochthonous signal by terrigenous detritus. These
differences distinguish normal hemipelagic sediment (Site
942) from active channel-levee sediment (Site 940) of the
Amazon Channel, where marine compounds represent a
background signal. The range of the ratio of two distinct
groups of lipids (i.e., terrigenous wax alcohols over
plankton-derived fatty acids) corresponds very well to
rough sedimentological estimates of sediment accumulation
rates, which vary, depending on location and sea level,
by more than 2 orders of magnitude. We suggest that this
approach can be utilized for a rough estimate of the
dilution of the autochthonous signal by terrigenous
detritus in environments such as the Amazon Fan.